1. Field of the Invention
The invention relates to methods for etching dielectric materials in plasma reactors.
2. Description of the Related Art
In the field of semiconductor material processing, vacuum processing chambers are used for the etching of materials and for chemical vapor deposition (CVD) of materials onto substrates. A radio frequency (RF) field is applied to process gases flowed into the processing chamber to generate a plasma. Exemplary parallel plate, transformer coupled plasma (TCP™), which is also called inductively coupled plasma (ICP), and electron-cyclotron resonance (ECR) reactors and components are disclosed in commonly-assigned U.S. Pat. Nos. 4,340,462; 4,948,458; 5,200,232 and 5,820,723.
During plasma etching, plasma is formed above the masked surface of the substrate by adding large amounts of energy to a gas at relatively low pressure, resulting in ionizing of the gas. By adjusting the electrical potential of the substrate to be etched, charged species in the plasma can be directed to impinge substantially normally upon the wafer so as to remove materials in unmasked regions of the substrate.
It is desirable to evenly distribute the plasma over the surface of substrates to achieve uniform etching rates over the entire substrate surface. For example, U.S. Pat. Nos. 4,595,484, 4,792,378, 4,820,371, 4,960,488 disclose showerhead electrodes for providing uniform gas flow to a semiconductor substrate.
A reactive ion etching system typically includes an etching chamber in which an upper electrode or anode and a lower electrode or cathode are positioned. The cathode is negatively biased with respect to the anode and reaction chamber walls. The substrate to be etched is covered by a suitable mask and placed on the cathode. A chemically reactive gas is introduced into the etching chamber and maintained at a selected pressure. The upper electrode includes gas holes through which process gas is dispersed into the reaction chamber. The electric field established between the anode and the cathode dissociates the process gas to form plasma. A surface of the substrate is etched by chemical interaction with the active ions and by momentum transfer of the ions striking the surface of the substrate. The electric field created by the electrodes attracts ions to the cathode, causing the ions to strike the substrate surface and remove material from the substrate.